Your ability to upgrade your cabin class will depend on the fare brand and type of ticket you purchase.
Economy Class and Business Class tickets purchased as Saver, Flex and Flex Plus fares can be upgraded online up to six hours before departure, except for Economy Class Saver tickets which can only be upgraded at online check-in between 48 and six hours before departure. Economy Class and Business Class Special fares aren’t eligible for upgrades with Skywards Miles.
You can upgrade online using Manage your booking. All upgrades are subject to seat availability and certain product restrictions.